In this study, we investigated the advantages and potential of de-oiled soy sauce residue as a superior raw material for the preparation of highly adsorptive microcrystalline cellulose (MCC), which was achieved employing a step-by-step chemical treatment. Acid hydrolysis conditions were optimized by one-factor-at-a-time and L₉ (3⁴) orthogonal array design methods. Under the optimal conditions (1:25 solid-to-liquid ratio, 2 mol/L HCl, 65 ℃ and 90 min), the yield and degree of polymerization (DP) of microcrystalline cellulose were 85.46% and 263, respectively. Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analyses indicated that the as-prepared MCC exhibited a cellulose I-like structure. Scanning electron microscopy (SEM) showed that the MCC particles were short rod-shaped, with numerous grooves on their surfaces. Compared with commercial MCC, this new MCC exhibited higher maximum degradation peak temperature (334 ℃), better water/oil-holding capacity (5.36 and 4.25 g/g), and stronger methylene blue adsorption capacity (73.15 mg/g). In conclusion, the MCC from soy sauce residue demonstrates strong biosorption capacity and has high application value.